iio:ad5755: Report scale as fractional value

Move the complexity of calculating the fixed point scale to the core.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/dac/ad5755.c

@@ -253,15 +253,6 @@ static inline int ad5755_get_offset(struct ad5755_state *st,
 	return (min * (1 << chan->scan_type.realbits)) / (max - min);
 }
 
-static inline int ad5755_get_scale(struct ad5755_state *st,
-	struct iio_chan_spec const *chan)
-{
-	int min, max;
-
-	ad5755_get_min_max(st, chan, &min, &max);
-	return ((max - min) * 1000000000ULL) >> chan->scan_type.realbits;
-}
-
 static int ad5755_chan_reg_info(struct ad5755_state *st,
 	struct iio_chan_spec const *chan, long info, bool write,
 	unsigned int *reg, unsigned int *shift, unsigned int *offset)
@@ -303,13 +294,15 @@ static int ad5755_read_raw(struct iio_dev *indio_dev,
 {
 	struct ad5755_state *st = iio_priv(indio_dev);
 	unsigned int reg, shift, offset;
+	int min, max;
 	int ret;
 
 	switch (info) {
 	case IIO_CHAN_INFO_SCALE:
-		*val = 0;
-		*val2 = ad5755_get_scale(st, chan);
-		return IIO_VAL_INT_PLUS_NANO;
+		ad5755_get_min_max(st, chan, &min, &max);
+		*val = max - min;
+		*val2 = chan->scan_type.realbits;
+		return IIO_VAL_FRACTIONAL_LOG2;
 	case IIO_CHAN_INFO_OFFSET:
 		*val = ad5755_get_offset(st, chan);
 		return IIO_VAL_INT;